The present application is based on and claims priority from Japanese Patent Applications Hei 11-367573 filed Dec. 24, 1999 and Hei 11-367580 filed Dec. 24, 1999, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a lead wire unit of a DC rotary electric machine, such as a DC motor or a DC generator that has a plurality of brushes.
2. Description of the Related Art
U.S. Pat. No. 4,965,478 or the corresponding Japanese Patent Application JP-Y2-6-35649 discloses a DC motor having four brushes. In this motor, a pair of stranded brush lead wires, which supplies battery current to a pair of brushes, is bundled and inserted into a grommet. The grommet has a pipe-like protecting portion that covers the lead wires extending outward from a motor frame. The protecting portion protects a portion of the lead wires between the motor frame and a metal joint that is connected to an outside power source. The plurality of lead wires extends outward from the grommet and fixedly welded to the metal joint at the ends thereof.
Although the lead wires that are disposed inside the frame is protected from vibration of the motor, the lead wire outside the frame is not well protected. In other words, if the metal joint vibrates relative to the frame, or if the lead wire extending outward from the frame is vibrated, the portion of the lead wire welded to the metal joint may snap off. This is because the welded portion of the stranded lead wire is fixed to the metal joint while the middle portion thereof is frequently bent at the metal joint. Because portions of the lead wire around the welded portion are repeatedly bent, the lead wire may snap off due to a fatigue failure.
For example, a starter motor for starting a vehicle engine is exposed to such a vibration condition. When the engine starts, a magnet switch shakes much relative to the starter motor. Accordingly a lead wire extending outward from the starter motor to the magnet switch is shaken repeatedly.
JP-A-10-215542 discloses a lead wire unit, in which lead wires extend through a grommet to connect an outside power source and a pair of brushes disposed in a frame.
In the above publication, because the lead wires extend through the grommet, there are many longitudinal gaps between the lead wires and the grommet. Accordingly, water may get into the inside of the frame through the longitudinal gaps.
There was an idea of fusing a portion of the lead wires inserted into the grommet by a welder. However it is difficult to make the peripheral portion solid enough to eliminate such longitudinal gaps and to form a watertight seal in the grommet, because such portion may change in shape and in size. This makes it difficult to design the inside diameter of the grommet for force-fit or interference-fit with the lead wires.
There was another idea of the grommet having as long sleeve as possible to provide a watertight seal. However, this long sleeve cannot seal out water passing through the longitudinal gaps as far as the lead wires are stranded wires.
Thus it is not possible to provide watertight seal by such conventional structures.
It is a main object of the invention to provide a lead wire unit of a rotary electric machine in which an outwardly extending lead wire is prevented from snapping off due to vibration.
According to a first feature of the invention is a lead wire unit that includes an outside power supply wire, an inside brush lead wire, and a metal joint. The power supply wire extends outward from the frame. The brush lead wire extends inside the frame and connected to a brush unit disposed inside the frame. The metal joint has terminals to which the power supply wire and the brush lead wire are welded. The grommet has a hollow portion and a holding portion. The metal joint is force-fitted to the hollow portion, and the holding portion holds a portion of the power supply wire near the metal joint.
Because the holding portion of the grommet holds the portion of the lead wire near the welded portion, the lead wire can be prevented from being bent repeatedly. As a result, the power supply wire is prevented from snapping off near the metal joint.
In addition, the power supply wire and brush lead wire are not inserted into the grommet but the metal joint is securely fitted into the through hole of the grommet. Different from a bundle of stranded lead wires, the metal joint has no longitudinal gaps or through holes therein. The metal joint has an outside terminal portion, an inside terminal portion and a portion that is force-fitted or interference-fitted to a hollow portion of the grommet. Therefore, the grommet provides a watertight seal even if the power supply wire and brush lead wire are formed of a large number of stranded wires having a plurality of longitudinal gaps. As a result, the DC rotary electric machine provides a highly watertight seal at the portion from which the lead wire extends outward.
According to a second feature of the invention, one of the grommet and the metal joint has a projection strip in close contact with the other under pressure to separate the power supply wire from the brush lead wire. Therefore, the inside space is water-tightly sealed from the outside space.
Another object of the invention is to provide a lead wire unit of a DC rotary electric machine that has a watertight seal at a portion from which lead wires extend outwardly.
According to a third feature of the invention, a lead wire unit includes outside power supply wire, a brush-lead wire connected to a brush unit, and a metal joint disposed between the outside power supply wire and the brush lead wire. The metal joint has an outside terminal to which the power supply wire is connected and an inside terminal to which the brush lead wire is connected at a portion spaced apart from the outside terminal, and is force-fitted to a hollow portion of the grommet.
In other words, neither the power supply wire nor the brush lead wire extends through the grommet, and only the metal joint is fitted in the grommet. The metal joint is a solid conductive member having no longitudinal gaps, and at least a peripheral portion of the metal joint is force-fitted to a hollow portion of the grommet between the outer terminal and the inner terminal of the metal joint. Therefore, even if the power supply wire and the brush lead wire are formed of stranded wires, the lead wire unit provides an excellent watertight seal.
In addition, the lead wire can be extended outwardly in a desired direction from the grommet by using a metal joint. Accordingly, it is very easy to connect the lead wires to an outside power source.
According to a fourth feature of the invention, the metal joint is formed of a T-shaped plate member having a longitudinal portion whose edge has the outside terminal and a lateral portion whose edge has the inside terminal.
Therefore, the longitudinal portion can be force-fitted into a through hole of the grommet so that excellent watertight seal can be provided between the metal joint and the grommet.
The lateral portion is much wider than the longitudinal portion. The lateral portion holds the metal joint at the circumferential portion of the grommet and prevents the metal joint from falling out of the grommet under a strong pull. In addition, the lateral portion can have a plurality of the inside terminals, which make connection work easier. The metal joint is a plate member, which is easy to manufacture at a low cost and easy to connect the outside power supply lead wire and the brush lead wires by welding.